This invention relates to electronic calculator timepieces or watches incorporating calculator apparatus integrally associated with said timepiece circuitry, and more particularly, calculator apparatus to be used in conjuction with electronic watch circuitry to enable a user to perform arithmetic and other calculations by means of a compact, "wrist watch" or similar configuration.
The electronic wrist watch operating with digital logic circuitry is a relatively recent development afforded by technological advances. There is a virtual plethora of patents and technical articles which describe such timepieces and the subsequent advantages of the electronic digital watch as compared to its mechanical counterparts.
The frequency stability of such watches exceeds that of the mechanical devices due to the fact that its operation is dependent upon an accurate quartz, crystal oscillator. The oscillator in such a watch generates an 8, 16 or 32 KHz reference signal, which is conventionally divided in frequency by means of digital divider circuits, as cascaded bistable multivibrators to provide a 1 Hz or other "time-keeping" signal. This signal (1 Hz) is then counted by digital counters to determine seconds, minutes, and hours. The counters are associated with gates and storage display circuits used to illuminate a visual display, such as light emitting diodes or liquid crystals.
These watches, besides being reliable and attractive, offer accuracies of 10 seconds or less per month, a significant advance over the minute-per-month accuracy of conventional mechanical watches.
Since such devices are powered by a small battery, power consumption is a primary consideration in the design and fabrication of such a watch. The plurality of such watches use C/MOS or complimentary MOS integrated circuits and certain use low power liquid crystal displays to conserve power and assure operation of such a watch for periods up to and exceeding one year without battery replacement. Thus, the watch as utilized consumes about 30 microwatts or less in power continuously for about one year, therefore permitting the use of a small 1.5 volt hearing aid type battery. The advantages of complementary metal-oxide semiconductor (C/MOS) technology in such an electronic watch is great in that it has very low consumption, very high noise immunity and good switching speeds; but suffers from relatively high cost. In any event, since a watch is a fairly expensive item and since the costs are continuously decreasing due to new technology, the operating characteristics of C/MOS logic is well worth the expense.
When one investigates the applicability of housing a calculator and associated circuitry in a common enclosure with an electronic watch, one is faced with extremely more difficult problems.
Primarily, a calculator or device capable of performing arithmetic operations and calculations of that sort requires extensive circuit components, far greater in complexity and component count than that required for a watch. Hence, it is not economically feasible to utilize C/MOS circuitry. Therefore, one is required to use a less expensive form of logic circuitry which has to be compatible and operate in conjuction with the C/MOS clock circuitry. Such a form of circuitry is designated as P-channel metal oxide circuitry or P-MOS logic circuitry. The advantages of P-MOS circuitry is cost and chip size. Where a comparison in price is possible, it is apparent that P-MOS is 50% or more less expensive than C/MOS. P-MOS fabrication generally requires about five masking steps in fabricating the integrated circuit, while C/MOS, which can be viewed as a combination of P-channel MOS technology and N-channel MOS technology requires seven to eight masking steps. Another major consideration between C/MOS circuitry is in integrated circuit chip area. A C/MOS circuit, especially one of the repetitive type, as a shift register, may require 50% more total area than a P-MOS circuit. Thus, as circuit configurations become large, as in a calculator, C/MOS will require greater chip sizes than P-MOS circuitry. In addition, C/MOS requires more contacts than P-MOS.
In any event, a major consideration in the implementation of a calculator watch is to use as much circuitry as possible in common between the C/MOS clock circuits and the P/MOS calculator circuits. Furthermore, due to the increased power requirements of the P-MOS, use the circuitry as little as possible and only when necessary. This is to conserve power and enable the user to obtain the maximum battery life possible, while gaining the advantages of affording him extreme versatility due to the unique configuration of a calculator watch.
It is therefore an object of this invention to provide an integral calculator watch apparatus utilizing low cost economical logic configurations while maintaining relatively low power consumption.